In 2008 Wall Street was close to meltdown. And the world economy was feeling the full force of a financial crash which changed long held assumptions about the stability of markets and global capitalism. HARDtalk's Stephen Sackur speaks to Ben Bernanke who was chairman of the Federal Reserve, the US Central Bank, at the time and took decisions then which continue to shape economic policy today. Can we be confident the right lessons have been learned from the great crash?